Autoinflammatory syndromes comprise a heterogeneous group of inherited disorders characterized by recurrent episodes of aseptic inflammation involving cells of the innate immune system. A hallmark of these disorders is the abnormal infiltration of neutrophils into tissues, suggesting that defects in neutrophil traffickin or motility may contribute to disease pathogenesis. Critical steps during the inflammatory response include leukocyte polarization and migration in the direction of chemoattractant. The long term goal of our work is to define signaling pathways that regulate neutrophil chemotaxis and to understand the implications of these mechanisms to the pathogenesis of chronic inflammatory disease by using zebrafish as a model system to examine neutrophil chemotaxis and inflammation in vivo. Knowledge of the basic mechanisms that regulate neutrophil chemotaxis should provide therapeutic targets for autoinflammatory syndromes and other disease states in which inflammation is central to pathogenesis, including heart disease, asthma, arthritis and inflammatory bowel disease. The strength of this proposal lies in the use of novel transgenic zebrafish lines that we have developed and the application of optogenetic tools to study neutrophil chemotaxis and inflammation in vivo. The hypothesis that guides this research is that neutrophil chemotaxis, mediated by the balance between reactive oxygen species (ROS), Src family kinases and tyrosine phosphatase signaling modulates the development and resolution of inflammation in vivo. We have made the following observations that support this proposal. 1. We recently discovered that hydrogen peroxide is an early signal that attracts neutrophils to wounds through the oxidation-mediated activation of the Src family kinase, Lyn. 2. We have developed optogenetic tools that allow the dissection of the molecular mechanisms that regulate neutrophil chemotaxis and bidirectional migration in vivo. 3. We were the first to report that neutrophils migrate away from wounds, in a process called reverse migration that may mediate local resolution of inflammation or may prime subsequent immune responses. 4. We have identified specific signaling molecules that mediate neutrophil reverse migration, including the tyrosine phosphatase SHP1 that has been associated with autoinflammation. We are now uniquely positioned to make rapid progress with the following Specific Aims: Aim 1. Elucidate how the Src family kinase, Lyn, regulates neutrophil chemotaxis and inflammation in zebrafish. Aim 2. Elucidate the role of reactive oxygen species (ROS) in the regulation of neutrophil motility and inflammation. Aim 3. Use zebrafish as a model system to study neutrophil chemotaxis in autoinflammation in vivo. The proposed work is innovative because of the application of live imaging and optogenetic tools to address fundamental questions about neutrophil motility during inflammation in zebrafish. The work is significant because of the potential to identify new strategies to control neutrophil-mediated inflammation in vivo, which plays a central role in the pathogenesis of many human diseases including cardiovascular disease, autoimmunity and cancer.